Palindrome
Description
Given a string s, determine if it contains any palindrome of length exactly 100 as a subsequence. If it has any, print any one of them. If it doesn't have any, print a palindrome that is a subsequence of s and is as long as possible.
The only line of the input contains one string s of length n (1 ≤ n ≤ 5·104) containing only lowercase English letters.
If s contains a palindrome of length exactly 100 as a subsequence, print any palindrome of length 100 which is a subsequence of s. If s doesn't contain any palindromes of length exactly 100, print a palindrome that is a subsequence of s and is as long as possible.
If there exists multiple answers, you are allowed to print any of them.
Input
The only line of the input contains one string s of length n (1 ≤ n ≤ 5·104) containing only lowercase English letters.
Output
If s contains a palindrome of length exactly 100 as a subsequence, print any palindrome of length 100 which is a subsequence of s. If s doesn't contain any palindromes of length exactly 100, print a palindrome that is a subsequence of s and is as long as possible.
If there exists multiple answers, you are allowed to print any of them.
Samples
bbbabcbbb
bbbcbbb
rquwmzexectvnbanemsmdufrg
rumenanemur
Note
A subsequence of a string is a string that can be derived from it by deleting some characters without changing the order of the remaining characters. A palindrome is a string that reads the same forward or backward.